What To Do When Your Cannabis Plants Grow Too Tall

Everybody loves big cannabis plants, but sometimes they can get too tall. This is bad news in a restricted space or for the stealth outdoor grower. Find out how to control your overeager marijuana plants with this informative blog from Royal Queen Seeds.

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25 Dec 2017

WHEN CANNABIS GROWS TOO TALL

When marijuana is exposed to prime growing conditions, it should fulfill its genetic potential. Sometimes, this means your plants will grow too tall. This can easily happen with sativas that stretch substantially or Kush varieties that tend to have generous distances between nodes. Some species of cannabis stretch notoriously when they enter the flowering phase, even doubling their vegetative height in some cases. Although the whole idea is to get the largest of plants with the heaviest yields of mature flowers possible, depending on the situation, plants that are too tall can be inconvenient.

Often, space is limited indoors and plants that are too tall can exceed the height of the grow space. If the grow room is a multi-strain grow, raising the lights to suit the taller plants can deprive shorter plants of sufficient lighting. Outdoors, especially in stealth grows, plants that are too tall can attract unwanted attention. Controlling the height of your marijuana plants is not very difficult and can be done in a number of ways. Here are a few techniques that can keep the height of your marijuana under control.

THINK AHEAD

If you are well aware that the strain you are growing is going to be tall, then height control starts in the early vegetative phase. Alternatively, the size of your grow space may require height control no matter the strain. Topping or fimming when plants are young encourages a shorter, but bushier plant. Grow room space still needs to be considered, however, as you are exchanging height for floor area.

Air circulation is a priority when plants become bushier in tight quarters. Controlling the height of your crop, only to suffer from mould or fungus due to lack of circulation is definitely a no-no. Lollipopping your plants will guarantee good air circulation below the canopy, preventing pathogens from taking hold. This also has the added bonus of chunkier and weightier colas come harvest, with less unwanted popcorn buds.

TRAINING

LST or low stress training is the art of gently tying the branches of your plants to grow more horizontally. Either the main stem is tied down, encouraging the side branches to be dominant, after which the side branches are also tied down; or the plants are topped a number of times and the new growth is tied down in the mainlining style. LST and mainlining have the benefit of exposing more of the plant to light, therefore encouraging weightier flowers all over.

What’s great about these techniques is an even canopy instead of one main cola. The extreme of this style is ScrOGging, in which the whole plant is encouraged to grow horizontally. A screen of netting is used to hold down all new growth until the plants form a mat. Appropriately called “screen of green,” one or two plants may fill an entire grow space.

PRE-FLOWER TOPPING

Letting your plants grow untouched during the vegetative phase, then topping just prior to flowering also controls height. When your plants are about to enter the flowering stage, top all branches. This has the effect of reining in the flower stretch. The plants are urged to produce new flower growth instead of focussing energy on stretching out.

Occasionally, pre-flower topping needs to be a full pre-flower pruning. If your plants fill the grow space during the vegetative phase, there is no way there will be enough room for flowering. It is time to get drastic. Aggressively prune the plants to half their size and switch lights to the 12/12 flower cycle. Don’t worry, cannabis is very hardy and can even recover from being reduced to a stalk with only one or two leaves remaining. Try not to beat yourself up about the loss of time and reduced final yields. All lessons are good lessons on the way to becoming a weed growing expert.

HUMIDITY

Cannabis plants transpire a substantial amount of water. Marijuana prefers a relative humidity (RH) of 50-65%. When they get too big, humidity can become a problem as the plants constantly release water vapor into the air. Water then gathers on leaves and other surfaces in the grow room, potentially causing mould and other issues. If humidity is becoming a problem, the use of a dehumidifier or increasing exhaust fan power can help. Defoliating can also increase airflow to control humidity. Remove lower and mid-level fan leaves only. This has the added benefit of increasing light penetration to the lower flowering branches.

TEMPERATURE

As with humidity, when plants get too big, temperature in the grow-op can rise. Reduced airflow and excessive height can drive up temperature and position plants too close to grow lights. Cannabis thrives when the temperature averages 25°C. When temps exceed this, plants are more likely to stretch. High temperatures can also affect leaf and flower formations, as well as final bud flavours and potency.

LIGHT INTENSITY

If your plants are getting too tall or too hot and you have the room, simply raise the grow lights as high as possible. Remember, lights that are too far from the tops of your plants can also cause stretching, so make sure to achieve the ideal light positioning.

Light intensity can be adjusted as a method for controlling growth speed and height. Some grow lights have adjustable outputs. If your plants are getting unruly, reduce the intensity. If you are using more than one lamp, simply turn some off.

During the flowering phase, growth can be controlled by reducing the photoperiod - but only if your plants have been flowering for at least six weeks. Reducing leaf production and stem stretching can be achieved by reducing the “lights-on” period from 12 hours to 11 or 10 hours.

CHOOSE WISELY

Appropriate strain choice can help avoid height issues before they even arise. If you have limited space, your dreams of cultivating a classic sativa will need to remain just that, dreams. Stout indicas and hybrids or autoflowering genetics can keep heights under control. Many autoflowering strains are ideal for indoor growing as they have relatively no vegetative period. Some strains will not grow taller than 50cm, but will still provide excellent yields per m².

DON’T WORRY, BE HAPPY

With a little bit of consideration and forethought, height need not be an issue when growing marijuana. Some research into strain characteristics is the first, very important step. Then, appropriate growing techniques will make sure you get lots of yummy buds with no drama. Happy growing!